In recent years, an increasing miniaturization of electronic and optical structural elements has taken place. In particular, the so-called mobile devices, i.e., electronic devices such as smartphones, mobile phones, notebooks and tablets, which have an increasingly greater electronic and optical functional range, are the driving force behind this development. The optical elements include at least one lens, but very often even of multiple lenses that are stacked on one another and that project the light beams onto an image sensor. In this case, the greatest value must be placed on the quality of the optical elements in order to obtain an image that is as sharp and undistorted as possible.
In principle, optical elements for the visible light spectrum can be manufactured from glass, in particular from SiO2, or from polymers. Glass is primarily suitable based on its excellent optical properties, especially because of its refraction index, specifically for the production of such lenses.
Nevertheless, to date, lenses for mobile devices are still produced predominantly from polymers. Polymers are embossed simply by an embossing process and a special die to form the desired lens shape and therefore to date still represent the preferred material for the lens production. In addition, the injection-molding technique is still widely used in the production of such lenses.
There are two large groups of production processes for the mass production of optical elements.
The first production process makes possible the embossing of multiple optical elements in a single embossing step. This group of production processes can in turn be divided into a subgroup of production processes that require a carrier substrate in order to emboss multiple, individual optical elements and into a subgroup that can completely dispense with a carrier substrate, since the optical elements are part of a so-called monolithic substrate that is produced in a completely interconnecting manner and in an embossing step between two dies. A monolithic substrate is thus defined as an embossing product, in which all embossed optical elements are connected to one another and form a large interconnecting field of optical elements. Since the optical elements are predominantly lenses and the substrates are in most cases circular, the embossing product is in most cases referred to as a monolithic lens wafer.
In the second group of production processes, multiple optical elements are not produced by a single embossing step but rather are produced individually, by a so-called step-and-repeat process. With this production process, the embossing of multiple, individual optical elements is possible. The optical elements are not connected to one another. In most cases, the optical elements are embossed directly on a carrier substrate. The optical elements can also be tightly connected to the carrier substrate, by which the carrier substrate obtains a functional property. The carrier substrate is then cut in a separating process along the free spaces between the optical elements. After the separating process, multiple composite optical elements comprised of a carrier substrate part and an optical element embossed thereon are obtained. This type of production process as well as the products developed therefrom are not discussed in more detail, however, in this patent specification.
In a third group of production processes, the embossing material is applied individually in multiple positions of a carrier substrate. Accordingly, a full-surface embossing process, which embosses the individual embossing materials specifically in the respective shapes but does not lead to a merging of the embossing materials, is carried out. As a result, it is possible to produce multiple optical elements at the same time on a carrier substrate. Such a process is described very precisely in the publication WO2013/178263A1.
Glass is actually defined as the very broad and general class of materials of amorphous, at times also partially crystalline, materials that are frozen in their glass-like state by a special production process.
While the production of macroscopic optical elements, in particular lenses, from glass for optical devices such as cameras, binoculars or telescopes in principle no longer represents a major challenge, the corresponding production of very small lenses from glass is to this day extremely problematic. The reason for this primarily lies in the fact that larger optical elements are ground predominantly from glass semi-finished products. The shaping is thus predominantly performed in the cold state. Such a shaping of optical elements, in particular lenses, is hardly feasible in the millimeter or micrometer range, however. In addition, conventional production methods for lenses that are used in modern devices are too expensive. In addition, in the industries of semiconductors, electronics and optics, the already mentioned monolithic substrates, therefore substrates of interconnecting optical elements, are preferred. A production of such a monolithic glass substrate is also extremely difficult with conventional methods. The use of a fully-automated micromilling cutter that processes a corresponding glass semi-finished product would be conceivable. This process has much too small a throughput, however, and therefore is not suitable for mass production. In addition, the surface of the optical elements on the glass substrate would be much too rough. The extreme roughness has a negative influence on the optical properties of the optical elements and is therefore to be avoided in principle or to be reduced to a minimum.
Nevertheless, in the industry, there exists a production process for monolithic glass substrates that is suitable for mass use. This is based on an etching technique, however, and not on mechanical fabrication. Below, the state of the art is explained in more detail relative to this etching technique in order to show how complicated, production-intensive and expensive the current manufacturing of monolithic glass substrates is.
In a first partial step, the coating of a selected glass substrate is carried out with a metal layer. In a second partial step, the metal layer is then coated with a photoresist, which, in a third partial step, has to be correspondingly structured by a mask and a photolithographic process. Then, the photoresist is removed by chemicals at the necessary spots and opens up access to the metal layer. In a sixth partial step, the structural transfer into the metal layer is carried out, followed by the removal of the photoresist. The metal layer is now used as a mask for the structuring of the actual glass substrate. The glass substrate is then etched by relatively toxic chemicals. In the last process step, the removal of the metal layer is finally carried out, in most cases in turn by other chemicals.
The necessary process steps for the structuring of such a glass substrate are extremely production-intensive, time-intensive, costly, and, primarily, based on chemicals that are very dangerous and toxic, and immensely harmful to the environment. In addition, a process that is complicated to such an extent with many partial steps is very susceptible to flaws.
In conclusion, it can be stated that in the state of the art, no noteworthy process, most particularly one suitable for mass use, yet exists for the production of monolithic glass substrates, in particular monolithic glass lens wafers, that be implemented economically, simply, and with as few chemicals as possible.
It is therefore the object of this invention to make available an improved method for the production of optical glass elements.